This is the POF Phoenix HP22 10-round magazine with a grip extension. This also fits HP22A pistols.

About POF

Patriot Ordnance Factory, also known as POF-USA, is a premier firearms manufacturer based in Phoenix, Arizona, United States. It was founded in 2002 by Frank DeSomma with the mission to deliver high-performing firearms that are reliable, accurate, and easy to maintain.

The company is highly respected in the gun industry for its innovation and commitment to excellence. They were among the first the first to bring a piston-operated weapon system to the AR platform, which can have advantages in terms of reliability and cleaning over the traditional direct impingement system.

POF-USA produces a variety of rifles and pistols, as well as components and accessories for firearms. Their products are designed for military, law enforcement, and civilian use. Offering a range of calibers and configurations, their notable models include the Revolution, Rogue, P415, and many others.